The present invention relates to a propulsion device with reusable pressure generating means, in particular for generating a liquid micro-jet for transdermal injection.
Manually operated syringes with needles are the most common form of hypodermic injection devices. They have the advantage of being reliable and low cost. The disadvantages are, inter alia, the risk of transmitting diseases by re-use of the syringe, and the pain felt by the patient.
In view of these disadvantages, there have been many attempts to provide needleless hypodermic injection devices in which a liquid to be injected is propelled at high speed by a pressure generator, thereby piercing the skin of a human or animal patient. Such devices are, for example, described in patent publications U.S. Pat. Nos. 3,537,212, 2,687,725, 4,596,556, 4,722,728, 4,874,367, 4,966,581, 5,501,666 and WO 98/41250. In order to ensure sterility and avoid contamination of medicaments to be injected, certain conventional devices as described in patents U.S. Pat. No. 4,874,367 and U.S. Pat. No. 4,966,581 comprise re-usable pressure generating mechanisms receiving disposable cartridges containing the liquid to be injected. The devices described in these patents are very complex and made of a large number of pieces. They are also bulky, costly and limited in their performance, particularly as concerns the injection pressure and jet diameter which are in the order of 70 bars or less and 100 to 330 μm, respectively, although initial peak pressure may attain around 300 bars. Insufficient pressure and a large diameter jet increases pain and the risk that only a portion of the medicament is injected, especially with respect to patients having a resistant skin. Moreover, the depth of administration of liquid is difficult to control accurately with conventional devices.
Considering the abovementioned disadvantages, an object of the present invention is to provide a re-usable propulsion device that is effective, reliable and compact. It is advantageous to provide a propulsion device for needleless transdermal administration of liquids. It is advantageous to provide an injection device that is safe to operate. It is advantageous to provide an injection device that eliminates the risk of disease transmission by re-use. It is advantageous to provide an injection device that is painless to use. It is advantageous to provide a propulsion system that enables the dosage to be varied. It is advantageous to provide a hypodermic injection device that is easy to use and cost effective.